A magneto-resistance effect device having a thin-film spin filter layer (SF) which is made of oxide or nitride and which is inserted in each of ferromagnetic layers or in an interface between each of the ferromagnetic layers and a nonmagnetic spacer layer has been proposed in JP-A-2004-6589. This SF layer can increase the MR (Magneto-Resistance) ratio because it has a spin filter effect in inhibiting conduction of either up-spin electrons or down-spin electrons.